Global Positioning Systems (GPS) units transmit GPS data using the Aeronautical Radio, Inc (ARINC) 743 or 743A protocols. These protocols are nearly identical except for the scaling of the Figure of Merit (FOM) terms. Currently, avionics system require the GPS installation (unit) to specify which type of ARINC protocol is used. However, if the GPS installation has been upgraded to use the ARINC 743A protocol, but the GPS installation is still reporting itself as using the ARINC 743 protocol, the outputted GPS data is improperly scaled. Improperly scaled FOM data can adversely affect avionic devices, such as an Enhanced Ground Proximity Warning System (EGPWS).
Therefore, there is a need to easily and cheaply determine the protocol type of GPS data.